In semiconductor device manufacturing, lithographic and etching processes are repeatedly performed to form patterned structures. For example, a photoresist layer may be firstly formed on a substrate to be processed, then exposure and development processes are performed to form openings in the photoresist layer. The substrate is exposed through the openings. Thereafter, the substrate is etched by using the patterned photoresist layer as a mask to form a desired pattern in the substrate.
In the development process, portions of the photoresist are exposed by light penetrating through a photo mask and the chemical characteristics of the exposed portions of the photoresist layer may be changed. In a case that a positive photoresist layer is used, the exposed portions are altered from insoluble to soluble. In a case that a negative photoresist layer is used, the exposed portions are altered from soluble to insoluble. Therefore, some portions of the photoresist layer are removed in the development process and the pattern on the photo mask is transferred onto the photoresist layer.
In a practical manufacturing process, the smallest distance between two neighboring components of a final device (the distance is named as “pitch”) depends on a resolution ratio of the exposure system. The smaller the ratio is, the smaller the pitch can be. With smaller pitch, semiconductor devices can be better integrated.
Conventional methods for reducing a pitch in a semiconductor device include use of a double patterning technology, which includes litho-etch-litho-etch (LELE) processes and dual-tone development (DDT) processes.
In a LELE process, two lithographic processes and two etching processes must be performed to one substrate to form a pattern thereon. Although the pitch between two neighboring components in the pattern may be obtained smaller, processing complexity is added because two lithographic processes and two etching processes must be performed.
In a DDT process, a photoresist layer is formed on a substrate and then exposed to form a dual pattern. Then, a positive-tone development and a negative-tone development are performed to the photoresist layer having the dual pattern therein. Such process is difficult to control because the positive-tone development and the negative-tone development may affect each other.
Therefore, there is a need to provide a double patterned structure and a simplified method for forming the double patterned structure with easy control of formation.